It is well known that steering or guidance of missiles and rockets can be accomplished by external aerodynamic surfaces such as fins or by vectoring of the rocket nozzle thrust. The thrust vectoring of rockets can be obtained with the use of either fluid dynamic means or mechanical means. The fluid dynamic guidance technique commonly referred to as secondary injection thrust vector control (SITVC), liquid injection thrust vector control (LITVC) or jet interaction (JI) employ injection of gas or liquid into the exhaust nozzle or external air stream through an appropriate surface. The mechanical techniques for rocket thrust vectoring can involve moving the nozzle exhaust bell by gimballing at the nozzle throat or jet tabs at the nozzle exit plane. The mechanical means for missiles use external movable fins such as those disclosed in U.S. Pat. Nos. 1,043,074 to Davis, 3,136,250 to Humphrey and 3,759,466 to Evers-Euterneck. Insertion of a solid body into the exhaust nozzle or external air stream can have the same effect as the fluid dynamic technique, but such may require the use of materials that are capable of withstanding the high temperature and possible erosive particulates in the adjacent gas stream.
U.S. Pat. No. 3,749,317 to Osofsky discloses an obstruction which may be reciprocated into the jet stream of a jet engine through activation of an explosive squib by electrical detonation. The Osofsky device is not controllably retractable and only has a one-time use.
An alternative to all of the foregoing for applications to a rocket nozzle is to employ an actively cooled body or strut that is inserted for a preascertained distance through the nozzle wall. The underlying basis for the technique is that injection of a gas or liquid on the interior of the nozzle wall causes a disturbance in the supersonic nozzle exhaust flow that in turn generates a shock wave inside the nozzle. Also associated with the gaseous or liquid injection is a separated flow region which generates a different, higher pressure than that on the diametrically opposite wall and therefore causes a thrust imbalance or offset. This force imbalance results in a turning moment and vectoring of the force generated by the rocket nozzle.
The nozzle exhaust stream can be composed of only high stagnation temperature gas (6000.degree. R) as is the case for liquid propellant rockets or scramjets or both high temperature gases and liquid and solid particulates. Materials do not exist that can survive the high temperature erosive gas exhaust stream for any long period of time (i.e. 30 seconds or longer). The presence of liquids from rocket propellant combustion products such as aluminum oxide create a more severe environment. This is because when the aluminum oxide liquid impacts the solid body, it solidifies and gives up its heat of condensation to the material. This causes local hot spots on the strut which can cause the strut to locally approach its yield stress and thereby cause pitting. Solid particles have a similar pitting effect on the strut surface.
For these reasons, in the prior art, liquid or gas streams were injected through the nozzle wall on demand to give the degree of thrust vector desired. These pure gas and liquid injection techniques required large amounts of consumable injectants and therefore have a tendency to increase missile weight and decrease payload.
It was to improve upon such prior art techniques that the present invention was evolved.